Treatment of catalyst in the chlorination of partially chlorinated hydrocarbons



tties Unite f This invention relates to an improved process for theproduction of chlorinated olefins by heating partially chlorinatedhydrocarbons in the presence of chlorine. It is particularly related tothe preparation of trichlorethylene and perchlorethylene fromtetrachlorethane.

The preparation of chlorinated olefins by thermal pyrolysis of partiallychlorinated alkanes is old and well known to the art. Furthermore, theproduction of perchlorethylene by heating a mixture of tetrachlorethaneand chlorine alone or in the presence of a catalyst was patented byBasel and Schaefier in 1938, US. Patent 2,139,219. Perchrlorethylene isproduced by the stoic'hiometrical reaction of one mol oftetrachlorethane with one mol of chlorine as indicated by the equation:

Basel and Schaeffer also disclosed the simultaneous production oftrichlorethylene and perehlorethylene by heat- .ing tetrachlorethanewith less than one molecular equivalent of chlorine. In these processes,the chlorethane containing reaction mixture is passed through heated orcatalytic reactors in the vapor state followed by condensation andrefining of the chlorinated products.

The efiiciency of these chlorethylene processes is reduced'by incompleteutilization of chlorine. This is particularly undesirable sinceunreacted chlorine contaminates the by-product hydrogen chloride andlimits its utility. Installation of a special purification step to remove chlorine from this material is undesirable since it addsappreciably to its cost. I

Copelin et al. application S.N. 755,150, filed August 15, 1958, now US.Patent 2,957,923 (October 25, 1960) discloses a process in whichtetrachlorethane and chlorine are passed through a heated open-tubereaction zone, preferably in the range 350 to 525 0, followed by anunheated zone which is packed with metal particles, such as stainlesssteel, nickel-chromium alloy, etc. This process improves chlorineconsumption and reduces formation of high boiling reaction by-products.It has now been discovered that chlorine consumption in this process canbe still further improved by subjecting nickel or nickel alloys,preferably nickel-chromium alloys, employed as a packing in the unheatedsecondary reactor to, a special activation treatment.

One of the objects of this invention is to improve chlorine consumptionin a process for the production of chlorinatedolefins by reactionofchlorine with a partially chlorinated alkane by contacting the reactinggases with a specially activated metal packing which serves as achlorination catalyst. An additional object is to improve chlorineconsumption in a process involving the reaction of tetrachlorethane withchlorine by use of a specially activated nickel or nickel alloycatalyst. A still further object is provision of an efficientchlorination catalyst consisting of activated nickel or nickel alloyparticles.

These objects are attained by treating a nickel or nickelalloy packing,used in a reactor for producing chlorinated olefins by the gas phasereaction of chlorine on partially chlorinated alkanes, to the action ofan oxygen-containing gas, preferably air and preferably in combinationwith steam, at temperatures of 350 C. or above. The pre- ECC ferredmetal packings for the process of this invention are composed of nickelor a high nickel alloy, particularly the nickel-chromium alloy knowncommercially as Inconel. The term high nickel alloy refers to an alloycontaining not less than 70% nickel. Inconel nickelchromium alloy isreported to contain 77% nickel, 15% chromium and 7% iron. The preferredtreating temperature is in the range 400 to 550 C. In general, thepreferred treating procedure involves heating with steam for about onehour, gradually adding air to the steam over an approximately 30-minuteperiod and then heating with air for three to six hours. However, itshould be noted that the time and order of treatment is not critical.Also, although a combination treatment with steam and air givesunexpectedly good results, a satisfactory activation can be obtainedwith the use of air alone. The nickel or nickel alloy packed reactorgradually becomes contaminated with carbon and solid reaction productson use which reduces the utility of the reactor and increases thepressure drop across the reactor. Treatment with air alone or incombination with steam burns out these impurities and improves chlorineconsumption in the reaction process. In this connection, it wasdiscovered that chlorine consumption improved progressively withsuccessive air or steam-air treatments until, under preferredconditions, consumption was approximately 100% after three or moresuccessive treatments. Prior to the use of the activation process ofthis invention, maximum chlorine consumption amounted to about whereasconsumptions ranging from about to quantitative can be achieved with theactivated metal packing.

Oxygen is the active ingredient in the air employed in the treatingprocess and any oxygen-containing gas may be employed provided thenon-oxygen portion of the gas is an inert diluent such as nitrogen,helium, carbon dioxide, etc. Pure oxygen may be used but its use 'in theabsence of an inert diluent is not recommended since, unless great careis employed in controlling temperatures and rate of addition,uncontrolled oxidation of carbon and solid chlorohydrocarbon impuritieswill take place. When this occurs temperatures well over 550 C. areproduced and tend to produce deformation and'metal creep in the reactor.Furthermore, hydrogen chloride liberated from solid chlorohydrocarbonsin the reactor may cause serious corrosion at these temperatures. Evenwith air, care must be used to avoid the development of hightemperatures and this can best be done by the procedure involvingpreliminary use of steam which is gradually mixed with air. The termoxygen-containing gas as employed in connection with this inventionmeans oxygen or any combination of oxygen and an inert gas preferablynitrogen. Steam is describedas a special oxygen diluent since its useresults in an unexpected improvement in the activated packing.

The invention is illustrated by the following experimental examples inwhich variously treated reactor pack- .ings were studied undersubstantially the same conditions. In these experiments, a mixture oftetrachlorethane and chlorine vapors containing approximately 10% byweight chlorine were passed through a heated cracking furnace followedby a packed reactor. In the cracking furnace the gases passed through92" of diameter nickel-chromium alloy Inconel tubes. The packed reactorconsisted of about 192" of 1" nickel-chromium alloy Inconel pipe. Thecracking furnace was maintained at a temperature of approximately 440 to460 C. whereas the temperature of the packed reactor ranged from about350 to 370 C. The feed gas was passed through the reactor system at arate of about 12 grams per minute.

XAMPLE 1 In this example, the packed reactor was filled with clean A"Inconel nickel-chromium alloy Raschig rings. A series ofchlorine-tetrachlorethane reactions were then carried out in thecracker-packed reactor system as previously described. Thesechlorination reactions ranged in length from about to 6 hours withproduction of perchlorethylene and trichlorethylene as the principalproducts. Unreacted chlorine was determined at intervals of 1.5 to 2hours throughout the reaction period by measuring the iodine liberatedfrom a potassium iodide solution through which the total product gas hadbeen bubbled for a two-minute period. Following each chlorinationreaction, the packing was subjected to a heat treatment with air or airplus steam. In Table I, the percent chlorine con- .sumptions and thepacking treatments preceding each re action are summarized.

Table I Packing Treatment Percent Reac- Chlorine Consumption tion ,No.

No. Time, Temp. Gas Individual Averhrs. degrees a Tests age None8887-87-83 86 1 8 4.50 Air 95-878387 88 2 4 450-500 Air 92-83-79 85 3 5500 Air 98999698 96 4 6 450 Air+ 100-100-100 100 Steam PrecedingReaction No. 5, the air-steam treatment of the packing comprised /2 hourair treatment, 1 /2 hours air plus steam and 4 hours air alone, all at450 C. It should be noted that this treatment even at a 50 lowertemperature than the previous air treatment made it possible to achievequantitative chlorine consumption.

EXAMPLE 2 This example was identical to Example 1 except that the packedreactor contained nickel rings cut from A diameter tubing. In addition,the first chlorination reaction was carried out in two approximately6-hour periods on consecutive days with air passing through the reactoras it cooled down and warmed up. The second chlorination ran for acomplete 10 hours while the last two were given the usual 5- to 6-hourperiod.

In the ease of nickel, more treatments are required before theactivation begins to take efiect than in the case of the Inconelnickel-chromium alloy of Example 1. However, it will be noted that afterthree treatments the chlorine consumption ranged from 94-96% in thefirst 3 to 4 hours as indicated by the first two chlorine consumptiontests which as previously stated were made after intervals of 1.5 to 2.0hours of operation.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows.

I claim:

1. In a process for the production of chlorinated ethylenes by reactionof chlorine with tetrachlorethane, the step for improving chlorineconsumption comprising contacting the reacting gases with a packingconsisting of particles of metal selected from the group consisting ofnickel and high nickel alloys which packing has been subjected to atleast three successive treatments with an oxygen-containing gas at atemperature over 350 C.

2. In a process for the production of chlorinated ethylenes by reactionof chlorine with tetrachlorethane in the presence of a packing ofparticles of metal selected from 'the group consisting of nickel andhigh nickel alloys, the steps for improving chlorine consumptioncomprising at least three periodic treatments of said packing with airat a temperature in the range 350 C. to 550 C.

3. In a process for the production of chlorinated ethylenes by reactionof chlorine with tetrachlorethane in the presence of a packing ofparticles of metal selected from the group consisting of nickel and highnickel alloys, the steps for improving chlorine consumption comprisingat least three periodic treatments of said packing with air and steam ata temperature in the range 350 to 550 C.

4. In a process for the production of chlorinated ethylenes by reactionof chlorine with tetrachlorethane in the presence of a packingconsisting of a nickel-chromium alloy consisting by weight ofapproximately 77% nickel, 15%, chromium, and 7% iron, the steps forimproving chlorine consumption comprising at least three periodictreatments of said packing with an oxygen-containing gas 'at atemperature in the range 350 C. to 550 C.

5. The process of claim 4 in which the packing is treated with anoxygen-containing gas and steam.

6. In a process for the production of chlorinated ethylenes by passing amixture of tetrachlorethane and chlorine containing approximately 10% byweight chlorine through a heated furnace followed by a reactorcontaining a packing of metal selected from the group consisting ofnickel and high nickel alloys, the steps for improving chlorineconsumption comprising at least three periodic treatments of saidpacking with air at a temperature in the range 350 C. to 550 C.

References Cited in the file of this patent UNITED STATES PATENTS

1. IN A PROCESS FOR THE PRODUCTION OF CHLORINATED ETHYLENES BY REACTIONOF CHLORINE WITH TETRACHLORETHANE, THE STEP FOR IMPROVING CHLORINECONSUMPTION COMPRISING CONTEACTING THE REACTING GASES WITH A PACKINGCONSISTING OF PARTICLES OF METAL SELECTED FROM THE GROUP CONSISTING OFNICKEL AND HIGH NICKEL ALLOYS WHICH PACKING HAS BEEN SUBJECTED TO ATLEAST THREE SUCCESSIVE TREATMENTS WITH AN OXYGEN-CONTAINING GAS AT ATEMPERATURE OVER 350*C.